Hit the "Control Panel" button in the task bar at the top of your window. The hit the "Edit Options" button. Scroll down and click the "Change Avatar" button. You can then either upload your pic or link to it with a URL. You must have over ten posts to have a custom avatar though, and it must be no more then 100 by 100 pixels or 20000 bytes (whichever is smaller). Resize your pic to accomodate this using a program like Photoshop or something along those lines...Microsoft Paint will work.
I don't know if this is even what you wanted, but I thought it was a nice pic, so I made it. Just save it on your computer and follow the directions from Hyside above. If you wanted something else, and don't have a way to resize it- then post it, and I can do it for ya.